A transmodulator is an apparatus used in the telecommunication field to convert a signal of a first type of transmission scheme into a signal of a second type of transmission scheme. Specifically, transmission scheme may be any combination of: modulation type coding scheme, encryption scheme, error detection and correction methods and every other feature incorporated in the transmission scheme.
Very Small Aperture Terminal (VSAT) is a satellite communication terrestrial unit that is used for satellite communications of data, voice and video excluding broadcast TV. VSAT units are often located in remote and inaccessible places and sometimes serve as the sole means of communications.
One of the most common uses for VSAT units is to supply Internet connectivity to remote places by configuring the VSAT units to employ Internet Protocol (IP) based communications. Such VSAT IP systems usually take the form of a Star configuration wherein one central location, sometimes referred to as a Satellite Hub, Hub server, Ground Station, or Gateway (hereinafter referred to as: “Hub” or “Hub server”) is located in a strategic place, in close proximity to the Internet service provider backbone, while multiple remote VSAT units are scattered under the satellite beam coverage area. Each and every VSAT unit is connected in turn, through resource management units, to the end users. VSAT IP communication may provide very high data transfer rates thus supplying the remote end users, some of them in developing countries having limited means, with high broadband Internet connectivity.
Presently, the common satellite communication standard in use for satellite communication is the DVB-S, with many of the existing VSAT units still employing it. In addition to the DVB-S many other IP-based satellite communication systems operate on non-propriety forward channel formats. For example, systems provided by HNS (Direct Way, IPoS), I-Direct as well as Gilat's Skystar Advantage. The DVB-S and the other non-propriety formats are hereinafter referred to in this application as ‘legacy format’ or ‘legacy signal’, and any referral to DVB-S include the non-propriety formats mentioned above and similar ones.
Recently, an advanced standard, the DVB-S2, has been ratified. This standard provides improved spectral efficiency, higher data transfer rate, better error correction methodology and many more benefits. Additionally, the DVB-S2, coming very near to the theoretical channel capacity limit (aka the Shannon limit) may well be the last significant DVB standard to emerge, at least from a data transfer rate perspective.
The problem is that due to important developments made in the DVB-S2, such as different modulation and different error correction schemes, it is not backwards compatible to the legacy standard. Thus, VSAT units employing legacy standards such as the DVB-S may not use it. Consequently, over the years IP service providers will have to replace large numbers of VSAT units in order to enable their end users to receive the new DVB-S2 standard. Needless to say, these replacements are costly and undesirable as the switch to DVB-S2 requires a total equipment replacement.
A dedicated transmodulator may, in certain circumstances, supply the legacy equipment with the required upgrade so that it may enable the use the advanced standard, thus avoiding the costly total equipment replacement.
Transmodulation techniques are already known in the art, including the conversion between the above-mentioned DVB-S2 and the DVB-S standards.
Patent applications US20050125839 and US20040244059 both applied by LSI Logic Corporation, disclose a DVB-S/S2 transmodulator unit providing baseband video signaling for a set-top box local loop connection that may, among other things, implement a continuous one-way communication channel. While addressing the general aspects of DVB-S/S2 transmodulation, these applications focus on broadcast television communication, hence the mentioning of a set-top-box and video signaling equipment. Various aspects of the advanced DVB-S2 standard are not addressed by these applications, specifically the establishment of an IP-based communication channel employing feedback used for quality control of the communication channel. Additionally, these applications require the incoming and outcoming carrier frequency of the modulated signal to be the same another characteristic of broadcast TV.
Patent application US20040161031 discloses a DVB-S/S2 conversion unit, referred to in this application as a signal transcoder. Here also, the transcoder focuses on symbol transfer rates and carrier signal frequencies that are typical to broadcast TV rather than IP based communication. By concentrating on DVB-S/S2 conversion for the use of broadcast TV, some important qualitative and quantitative developments of the advanced DVB-S2 are overlooked and not addressed and so, the conversion offered by this application is narrow and limited and may not be used in IP based communications.
In view of the prior art it would be important to note that while the costs of a DVB-S/S2 transmodulator may top the costs of a new DVB-S2 compatible set-top-box for a TV, the costs of a DVB-S/S2 transmodulator for the use of VSAT unit would be marginal to the costs of a new DVB-S2 compatible VSAT. Therefore, it would be advantageous to have a DVB-S/S2 transmodulator that is optimized for VSAT networks, and is installed in the signal path before the VSAT unit. By this, Internet service providers will be able to reduce the costs of DVB-S2 introduction and the migration process at large will become simple.